The goal of this project is to define on a molecular level the genetic basis for the disease of chronic lymphocytic leukemia. Using lymphocytes from CLL patients, loss of heterozygosity measurements are being used to map molecular defects specific to CLL patients. The mouse NZB model, which is considered to be animal model for B-CLL is being used to generate simple sequence length polymorphisms to define the lesions in a mouse model. Chronic lymphocytic leukemia is one of a large number of hematologic malignancies which are being treated by monoclonal antibodies and cytokine products. Understanding of the molecular lesion of CLL will to design measurements useful for monitoring the effects of such therapies.